The working principle and structure of ultrasonic liquid level sensor

Working principle  

Ultrasonic sensors are sensors developed using the characteristics of ultrasonic waves. Underwater ultrasonic transducer is a mechanical wave with a higher vibration frequency than sound waves. It is generated by the vibration of the transducer chip under the excitation of voltage. It has high frequency, short wavelength, small diffraction phenomenon, especially good directionality, and can be directed into rays. Dissemination and other characteristics. Ultrasonic waves have a great ability to penetrate liquids and solids, especially in solids that are opaque to sunlight. It can penetrate to a depth of tens of meters. When the ultrasonic wave hits the impurity or the interface,piezoelectric ultrasonic transducer will produce a significant reflection to form an echo, and it can produce a Doppler effect when it hits a moving object. Therefore, ultrasonic testing is widely used in industry, national defense, biomedicine and other aspects. Ultrasound is used as a detection method, and it is necessary to generate and receive ultrasonic waves. The device that accomplishes this function is an ultrasonic sensor, which is habitually called an ultrasonic transducer, or an ultrasonic probe. 

Structure and composition  

ultrasonic transducer depth measurement is mainly composed of piezoelectric wafers, which can transmit and receive ultrasonic waves. Low-power ultrasound probes are mostly used for detection. It has many different structures, which can be divided into straight probe (longitudinal wave), oblique probe (transverse wave), surface wave probe (surface wave), lamb wave probe (lam wave), double probe (one probe reflection, one probe reception) Wait. The core of the ultrasonic sensor is a piezoelectric chip in its plastic or metal jacket. There can be many kinds of materials that make up the wafer. The size of the wafer, such as diameter and thickness are also different, so the performance of each sensor is different, we must know its performance before use. 

Main performance indicators of ultrasonic sensors

(1) Operating frequency. The working frequency is the resonance frequency of the piezoelectric wafer. When the frequency of the AC voltage applied to its two ends is equal to the resonance frequency of the chip, the output energy is the highest and the sensitivity is the highest. 

(2) Working temperature. Because the Curie point of piezoelectric materials is generally relatively high, especially when the ultrasonic probe used for diagnosis uses low power, the working temperature is relatively low, and it can work for a long time without failure. Medical ultrasonic sensors have relatively high temperatures and require separate refrigeration equipment. 

(3) Sensitivity. Mainly depends on the manufacturing wafer itself. The electromechanical coupling coefficient is large and the sensitivity is high; on the contrary, the sensitivity is low. 

Like ultrasonic sensors, a composite vibrator is flexibly fixed on the base. The composite vibrator is a combination of a resonator and a bimorph element vibrator composed of a metal sheet and a piezoelectric ceramic sheet. The resonator is in the shape of a horn, and the purpose is to effectively radiate the ultrasonic waves generated due to vibration, and to effectively concentrate the ultrasonic waves in the center of the vibrator. 

Ultrasonic sensors for outdoor use must have good sealing properties to prevent the intrusion of dew, rain and dust. Piezoelectric ceramics are fixed on the inside of the top of the metal box. The base is fixed to the open end of the box and covered with resin. For ultrasonic sensors used in industrial robots, it is required to have an accuracy of 1 mm and strong ultrasonic radiation.